1. Field of the Invention
The present invention relates to a chemically amplified resist composition and a manufacturing method of a semiconductor integrated circuit device wherein such a chemically amplified resist composition is utilized.
2. Description of the Related Art
The recent advance in the degree of integration in the semiconductor integrated circuit has put the ULSI (Ultra Large-Scaled Integrated circuit) into practical use. The technology to produce the ULSI has been attained through the progress in the miniaturization of conductive interconnections, electrodes and the like, and the minimum pattern currently in practical use is in the submicron range of 0.14 μm, while the minimum pattern aimed to attain at the moment is of 0.08 μm. Accompanying the miniaturization, the change in the light beam used for the exposure in the resist pattern formation has been taking place, from the ultraviolet rays conventionally utilized to the radioactive rays such as far-ultraviolet rays, electron rays and X-rays, with its wavelength shifting to a shorter region.
The chemically amplified resist is a very resist material that can stand the use under these shorter wavelengths and is used as such.
With the chemically amplified photoresist, its irradiated section is made soluble in an alkaline developer solution through a chemical reaction that is catalyzed by an acid generated from an acid generator by irradiation. Some chemically amplified photoresists provide positive patterns and the others, negative patterns.
In the case of the chemically amplified positive resist, the resist wherein a photo acid generator (PAG) is mixed into polymers is used, and the exposure (irradiation) of the chemically amplified positive resist sets off chain-reacting elimination reactions or hydrolytic reactions in the polymers, with a Brnsted acid generated from the photo acid generator by exposure acting as a catalyst, forming hydrophilic groups in the polymers and rendering the exposed section soluble in the alkaline developer solution, and thereby a positive resist pattern is formed.
In the case of the chemically amplified negative resist, the resist wherein a cross-linking agent and a photo acid generator are added and mixed into polymers which are soluble in the developer solution is used. With a Brensted acid generated from the photo acid generator by exposure acting as a catalyst, the exposure sets off chain-reacting cross-linking reactions in the polymers, making them to have larger molecular weights, and, at the same time, the polar groups thereof nonpolar by cross-linking so that the exposed sections are made insoluble in the developer solution, and thereby a negative resist pattern is formed.
In the case of the chemically amplified positive resist, however, the photo acid generator itself may be dissociated by exposure and the acid concentration in the vicinity of the resist surface is increased, giving rise to a problem that the pattern takes the form of a taper.
Meanwhile, in the case of the chemically amplified negative resist, the photo acid generator itself may be dissociated by exposure and the acid concentration in the vicinity of the resist surface is increased, giving rise to a problem that the top section of the pattern becomes overhanging in shape.
To overcome such problems, it has been known that the basic compound can be added into the chemically amplified resist with the object of controlling acid diffusion. Since the added basic compound is considered to quench the acid which is generated from the photo acid generator by irradiation, it is generally called a quencher. The addition of the quencher suppresses the formation of the surface layer of low solubility and leads to improvements in various aspects such as the sensitivity, the resolution, the pattern shape and the process stability.
Along with the progress in the miniaturization, a variety of compounds are even now being developed as a quencher and Japanese Patent Application Laid-open No. 100400/2001 and WO No. 004706/2001 disclose some of them.
In Japanese Patent Application Laid-open No. 100400/2001, there is selected a compound with an annular frame containing at least one nitrogen atom, which can be decomposed by an acid generated from a photo acid generator by exposure to form an acid weaker than the original acid. Further, in WO No. 004706/2001, there is given an amine derivative having a specific basicity as a quencher.
Now, referring to the drawings, a method of manufacturing a semiconductor integrated circuit device wherein an ordinal trench interconnection is utilized is described below.
FIG. 2 shows one example of a conventional manufacturing method of a via hole first type dual damascene interconnection.
First, a coating of a first anti-reflection film (not shown in the drawings) is applied onto the entire surface of a substrate wherein a first etching barrier film 7, a first interlayer insulating film 6, a second etching barrier film 5, a second interlayer insulating film. (a low-dielectric-constant film) 4 and a cap film (an insulating film) 3 are formed on a Cu lower layer interconnection layer 8, in this order, from the side of the substrate, and a first photoresist pattern (for via hole formation) is formed on the surface of the first anti-reflection film. Subsequently, using this first photoresist pattern as an etching mask, the first anti-reflection film, the cap film 3, the second interlayer insulating film 4, the second etching barrier film 5 and the first interlayer insulating film 6 are selectively etched in succession till the first etching barrier film 7 is exposed, and thereby a via hole 21 is formed (See FIG. 2(a)).
For the damascene interconnection structure, because Cu is utilized as the interconnection metal, the acid cleaning cannot be employed after etching of the via hole on the grounds that this cleaning, through the via hole which has been just made open, may cause oxidation of the metal used in the interconnection. Yet, ashing alone cannot remove etching residues thoroughly. The organic peeling-off is, therefore carried out after the step of ashing, using an organic peeling agent.
Next, after the first anti-reflection film and the first photoresist pattern are removed with ashing and the use of the organic peeling agent (See FIG. 2(a)), a second anti-reflection film 2 is formed over the entire surface of the substrate (in such a way that the via hole 21 may not be filled up completely) (See FIG. 2(b)) and a coating of a photoresist 1 is applied onto the surface of the anti-reflection film 2 (See FIG. 2(c)). With exposure being applied onto the coating of the photoresist, a second photoresist pattern 1 (for interconnection trench formation) is formed (See FIG. 2(d)) and, then, using this as an etching mask, the second anti-reflection film 2, the cap film 3 and the second interlayer insulating film 4 are selectively etched in succession till the second etching barrier film 5 is exposed (See FIGS. 2(e) and (f)), and thereby an interconnection trench 22 is formed.
Next, after the second anti-reflection film 2 and the second photoresist pattern 1 are peeled off or removed with ashing and the use of the organic peeling agent, the exposed first etching barrier film 7 is etched by the etch back method till the Cu lower layer interconnection layer 8 is exposed (See FIG. 2(g)). Next, following the cleaning of the substrate where a part of the Cu lower layer interconnection layer 8 is exposed a seed film and a metal barrier film are formed on the substrate, and thereafter a Cu plating film 9 is grown so as to fill up the via hole and the interconnection trench. After that, carrying out the CMP (Chemical Mechanical Polishing), the Cu plating film 9 and the cap film 3 are planarized (till the cap film 3 becomes almost completely removed) (See FIG. 2(h)). A dual damascene interconnection 9 that is electrically connected with the Cu lower layer interconnection layer 8 is thereby formed.
However, when the second photoresist pattern 1 is formed using a conventional chemically amplified positive photoresist composition, there arises a problem that the photoresist within the via hole 21 (as well as in its vicinity) may remain even after the exposure and the development are carried out.
To the positive resist, this phenomenon corresponds to the lowering of the sensitivity of the photoresist in part.
The cause to bring about such a problem is, in the present inventors' view, as follows. When application of coatings of an anti-reflection film and a chemically amplified photoresist composition and the exposure thereto are made without any pretreatment (heat treatment, UV treatment, oxygen plasma treatment or such), contaminants such as basic compounds and the moisture which are attached onto or seeped into the substrate surface (such as the wall surface of the via hole in the interlayer insulating film) may pass through the anti-reflection film and permeate into the photoresist in baking (a pre-bake: for removing the solvent) of the anti-reflection film and the photoresist.
In other words, because a deep opening and a deep trench are formed in the via hole first type dual damascene method, residues formed at the time of dry etching cannot be removed by ordinary cleaning methods. Therefore, an alkaline organic peeling agent including an organic amineis employed to accomplish thorough removal.
The contaminants such as basic compounds (amine components) contained in this organic peeling agent, the moisture and floating basic substances in the air become concentrated by attaching onto or seeping into the wall surface (interlayer insulating film) of the via hole. After that, when coatings of an anti-reflection film and a photoresist (a chemically amplified positive photoresist composition) for the interconnection trench are applied onto the substrate surface including the wall surface of the via hole, and pre-bake is conducted, the contaminants which become concentrated by attaching onto or seeping into the wall surface of the via hole permeate into the photoresist from the wall surface of the via hole, passing through the anti-reflection film. On irradiation, the permeated contaminants (such as amine components) neutralize the catalyst acid (H+) generated by photolysis of the photo acid generator contained in the photoresist (chemically amplified positive photoresist). The neutralization of the catalyst acid with these contaminants deactivates (becomes short of) the acidic catalysts in the photoresist (which is called the poisoning).
The photoresist in the region where the acidic catalysts are deactivated becomes incapable of undergoing a change (polarity change) to convert into a substance soluble in the developer solution. (For instance, a protecting group such as an acetal group becomes deblocked so that a chain reaction to form a hydroxyl group becomes difficult to take place). The photoresist in the region (within the via hole or in its vicinity) where the conversion into a substance soluble to the developer solution does not occur remains without dissolving. This makes the resist pattern within the via hole or in its vicinity have defective resolution.
Further, the experiments conducted by the present inventors showed that, with conventional chemically amplified resists, if the condition allowed the poisoning to occur, the development performed for 30 seconds could provide good resist patterns in the absence of the via hole but the resist pattern formed thereby around the via holes had faulty resolution due to severe poisoning. Although the resistance against poisoning could be raised by extending the development time period to 60 seconds, the resulting resolution remained insufficient.
Further, the experiments by the present inventors revealed such a problem (faulty resolution) became more marked if, in place of conventional silicon oxide films, low-dielectric-constant insulating films (Low-k films; for example, the dielectric constant <3.0) were utilized for the first interlayer insulating film 4 and the second interlayer insulating film 6. That is, when low-dielectric-constant insulating films were used, there arose a problem that the region where the photoresist remained without dissolving in the developer solution (the photoresist remained unresolved even though having subjected to the exposure) expanded.
This sort of the problem is considered by the present inventors to result from a fact that the low-dielectric-constant films (Low-k films) are often porous films whose molecular structure have spatial gaps and moreover, because these gaps (fine holes) tend to increase for the substances with lower dielectric constants, more contaminants become liable to attach onto (adsorb) or seeped into for the low-dielectric-constant films than for the ordinary interlayer insulating films (SiO2). As a result, the amount of contaminants to permeate into the photoresist from the low-dielectric-constant film becomes greater than that from the silicon oxide film and the region where the resist pattern has poor resolution expands.
The remaining photoresist of this sort covers circumference section of the via hole on the surface of the cap film 3, and, when the interconnection trench 22 is formed by etching, the remaining photoresist becomes halo-like on the cap film 3 so that a tapering cylindrical projection 10 made of the cap film 3 or the second interlayer insulating film 4 is formed in peripheral region of the via hole (See FIG. 2(g)). In the case that the low-dielectric-constant films (Low-k films) are employed for the interlayer insulating films, the projection 10 becomes larger. If formation of the Cu dual damascene interconnection 9 is carried out, while such a projection 10 remains, the presence of the projection 10 brings about separation or faulty connection between the via plug section and the interconnection section in the dual damascene interconnection 9 and, thus, results in unsatisfactory electrical connection between the via plug section and the interconnection section in the dual damascene interconnection 9 (See FIG. 2(h)). Accordingly, the reliability of the semiconductor device deteriorates.